GB692985A - Improvements in or relating to x-ray apparatus - Google Patents

Abstract

692,985. X-ray apparatus. WESTING- HOUSE ELECTRIC INTERNATIONAL CO. March 26, 1952 [April 14, 1951], No. 7732/52. Class 98 (i). [Also in Group XL (b)] Apparatus in which an electron beam produces on a luminescent output screen of an image intensifier a replica of an image produced by X-rays on an input screen, is characterized by means for impressing an intermittent control voltage on a control element of the image intensifier so as to produce and suppress alternately the image on the output screen electrically to provide intermittent exposures for a photographic sheet moving through the plane in which an image of the output screen is formed by a lens. As shown, an image intensifier 3 (e.g. of the kind described in Specification 680,404, [Group XL (a)], has at one end a screen 11 containing luminescent material such as zinc sulphide, on which an X-ray image is formed. The image causes electrons to be emitted from a closely adjacent layer of antimony activated with caesium, and the electrons are focused as by cylindrical electrodes 12, 13, 14, 15 on a screen 4 of luminescent material covered with a thin layer of aluminium. Screen 11 is at earth potential, and the coating of screen 4, and the electrodes 12, 13, 14, 15 are connected to a potential divider 16. The image on screen 4 is projected by a lens 5 on to a film 28 driven by sprockets 26, 27. Driving means 25 move film 28 either continuously or intermittently, and also actuate a pulse generator 24 which produces a pulse whenever a fresh area of film is fed to the film gate. This pulse operates a square-wave generator 23, the output from which is passed to a pulse transformer 17, which produces a positive-going pulse which is applied to the coating of screen 4 and to the electrodes of the intensifier. As long as the pulse lasts a properly focused image appears on screen 4 and is projected on to the film 28, but when the pulse ends the image is defocused or blacked out. Alternatively, electrode 12 only, or a control grid replacing it, may be held at such a negative potential that no electrons reach the screen 4, and the negative bias is raised to a positive potential by the pulse generator when the image is to be photographed. In a modification, where the images are produced at high speed, the film has marginal perforations and runs continuously. A narrow light beam is directed through the perforations on to a photoelectric cell, and the pulses so produced are fed to the square-wave generator 23. The image on screen 11 may be formed by penetrative radiation other than X-rays, e.g. by a beam of neutrons or like particles.